1. Field of the Invention
This invention is related to a carrier phase control apparatus used in a receiver apparatus (MODEM) adapted to demodulate a data signal modulated with a carrier signal through, for example, quadrature amplitude modulation and more particularly to an apparatus adapted to correct a carrier signal for a phase jitter having a 50 Hz (or 60 Hz) wave component, presumably leaking from the commercial power supply, and its harmonic wave components.
2. Description of the Prior Art
In order to reproduce data from a received data signal subject to phase modulation such as quadrature amplitude modulation, a carrier signal identical to a carrier with which the received data signal is modulated must be regenerated and many apparatuses for carrier recovery have been known.
A significant problem encountered in the carrier recovery is that a transmitted carrier signal suffers from a phase jitter due to a 50 Hz (or 60 Hz) wave component presumably leaking from the commercial power supply and its harmonic wave components.
An apparatus for eliminating a phase jitter has been known as disclosed in JP-A-53-54955, wherein a phase-modulated received signal is demodulated into a base band signal which in turn is equalized by an automatic equalizer, and a predictive filter predicts a carrier phase jitter on the basis of the equalized signal, to produce an output signal which is used to eliminate the carrier phase jitter. However, in the known apparatus, a two-dimensional automatic equalizer of transversed type is used as the predictive filter. Therefore, for the sake of suppressing the carrier phase jitter accurately and sufficiently, the necessary number of taps of the transversal filter is for example, about 30 or more. Accordingly, an arrangement to this end becomes complicated and can hardly be adapted for high-speed processings.